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<head><meta charset="utf-8"><title>fploat cast issue · t-compiler/wg-llvm · Zulip Chat Archive</title></head>
<h2>Stream: <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/index.html">t-compiler/wg-llvm</a></h2>
<h3>Topic: <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/fploat.20cast.20issue.html">fploat cast issue</a></h3>

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<a name="190156983"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/fploat%20cast%20issue/near/190156983" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> RalfJ <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/fploat.20cast.20issue.html#190156983">(Mar 10 2020 at 10:02)</a>:</h4>
<p>At <a href="https://github.com/rust-lang/rust/issues/69532" target="_blank" title="https://github.com/rust-lang/rust/issues/69532">https://github.com/rust-lang/rust/issues/69532</a> we have an issue in rustc const-eval that originates in librustc_apfloat which in turn is a direct port of LLVM's apfloat -- so likely this is an LLVM issue. Does someone here know enough about apfloat to turn this into an upstream issue?</p>



<a name="190157124"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/fploat%20cast%20issue/near/190157124" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/fploat.20cast.20issue.html#190157124">(Mar 10 2020 at 10:04)</a>:</h4>
<p>cc <span class="user-mention" data-user-id="119009">@eddyb</span></p>



<a name="190169692"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/fploat%20cast%20issue/near/190169692" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/fploat.20cast.20issue.html#190169692">(Mar 10 2020 at 13:15)</a>:</h4>
<p><span class="user-mention" data-user-id="120791">@RalfJ</span> I know either <a href="https://github.com/llvm/llvm-project/blob/eb812efa12fb82ca338794fa18b610ca9581aef5/llvm/lib/Support/APFloat.cpp#L2177-L2188" target="_blank" title="https://github.com/llvm/llvm-project/blob/eb812efa12fb82ca338794fa18b610ca9581aef5/llvm/lib/Support/APFloat.cpp#L2177-L2188">https://github.com/llvm/llvm-project/blob/eb812efa12fb82ca338794fa18b610ca9581aef5/llvm/lib/Support/APFloat.cpp#L2177-L2188</a> or <a href="https://github.com/llvm/llvm-project/blob/eb812efa12fb82ca338794fa18b610ca9581aef5/llvm/lib/Support/APFloat.cpp#L3196-L3198" target="_blank" title="https://github.com/llvm/llvm-project/blob/eb812efa12fb82ca338794fa18b610ca9581aef5/llvm/lib/Support/APFloat.cpp#L3196-L3198">https://github.com/llvm/llvm-project/blob/eb812efa12fb82ca338794fa18b610ca9581aef5/llvm/lib/Support/APFloat.cpp#L3196-L3198</a> should be changed (it's probably up to LLVM ppl to pick which), but I try to avoid interacting with upstream, it's a bit of a headache and I'm not set up to not lose track of it, that's why I cc'd <span class="user-mention" data-user-id="123586">@nagisa</span> and <span class="user-mention" data-user-id="133224">@Nikita Popov</span></p>



<a name="190169745"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/fploat%20cast%20issue/near/190169745" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/fploat.20cast.20issue.html#190169745">(Mar 10 2020 at 13:16)</a>:</h4>
<p>(oh, and, unlike the Rust code, there are several copies of the latter piece of code, for each float format)</p>



<a name="190236819"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/fploat%20cast%20issue/near/190236819" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/fploat.20cast.20issue.html#190236819">(Mar 10 2020 at 23:26)</a>:</h4>
<p>I have no idea what to write to them without taking time to investigate this</p>



<a name="190236828"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/fploat%20cast%20issue/near/190236828" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/fploat.20cast.20issue.html#190236828">(Mar 10 2020 at 23:26)</a>:</h4>
<p>and/or digest what has already been written</p>



<a name="190236848"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/187780-t-compiler/wg-llvm/topic/fploat%20cast%20issue/near/190236848" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nagisa <a href="https://rust-lang.github.io/zulip_archive/stream/187780-t-compiler/wg-llvm/topic/fploat.20cast.20issue.html#190236848">(Mar 10 2020 at 23:26)</a>:</h4>
<p>And I won’t have time for it before next weekend.</p>



<hr><p>Last updated: Aug 07 2021 at 22:04 UTC</p>
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